Vertebral compression fracture (VCF) can occur when a vertebral body is too weak to support a load and the spine collapses. A VCF may cause the spine to shorten, leading to spinal deformities and altering spinal biomechanics. Collapse may result in thoracic and lumbar spinal deformity and is often seen in elderly people. The spinal deformity, commonly known as a Dowager's Hump, is also referred to as kyphosis. Several causes can lead to a VCF, including osteoporosis, cancer or a traumatic incident, such as a fall or car accident.
A treatment for a VCF can involve injecting a material into vertebra, either at low or high pressure. Optionally, a surgical balloon can first be inserted into a vertebra and expanded to restore a collapsed vertebra to its original shape. A material can then be inserted into the restored vertebra, which, upon hardening, can maintain the original shape of the vertebra. The technique of inserting a material into a cavity, such as a collapsed vertebra, can also be used to treat other medical conditions, for example, in knee or hand joints.
Surgeons commonly use bone cement in order to fill voids in bone. It is desirable to use bone cement, such as an adhesive bone cement, to hold small bone fragments in place to allow for healing, when methods such as traditional plate and screw methods of reattachment are not feasible. Only a small amount of bone cement may be required to fill small gaps between the bone fragments in order to glue the fragments together. For example, volumes of cement under one cubic centimeter may be used. In such applications, the cement material may be delivered to the repair site through a delivery system, such as a syringe having a cannulated needle.
The bone cement may be a mixture of different ingredients, and, before applying the bone cement to a repair site, the cement may be prepared by mixing it in a bowl with a pestle. Prepared bone cements can have various viscosities, and some may have quite a high viscosity, with a consistency like a tacky paste. For example, typical adhesive bone cement may have a viscosity greater than 80 Pascal-seconds. The prepared bone cement can be transferred to the syringe through the opening in the proximal end of the syringe, which is made accessible by removing the plunger from the syringe.
The prepared cement material can be difficult to pour into the proximal end of an application syringe, especially when it has a high viscosity. Additionally, the opening at the proximal end of the syringe may be quite small, thus making the pouring of the bone cement into the syringe even more difficult. The pouring of the bone cement into the proximal end of the syringe can also be time consuming, which can be problematic when the curing time for the cement is relatively short. Furthermore, the material that is poured into the proximal end of the syringe can develop air pockets along the syringe barrel. Air pockets can detrimentally cause pressure spikes during injection of the cement. These pressure increases can cause filter pressing, where the liquid portion of the cement separates from the powder portion. This can result in the liquid being squeezed out of the syringe, leaving behind a dense mass of powder, which can jam the syringe.